The fuel flow to the combustor of a gas turbine engine is generally controlled by a mechanical valve which is responsive to a signal from a central computer control for the engine. Where such an engine is used in an aircraft, there is a critical need for continuous fuel flow inspite of a failure of the computer control. For this reason, the fuel flow unit is constructed with a failure mode of operation which is initiated by the absence of a fuel flow signal from the computer. In the failure mode the fuel flow unit will provide a predetermined amount of fuel flow in order to keep the engine running. This works fine when a computer failure occurs in flight, but there are instances where a failure may arise prior to start-up. The fuel flow called for in the failure mode is much greater than is required for normal start-up and idle operation. If the pilot is unaware of the failure, his normal ignition procedure could result in an explosion, fire, or severe over temperature. For this reason, it is the purpose of this invention to provide a means by which the ignition circuit is deactivated when a computer failure to the fuel control unit exists prior to engine start-up.